Legalese: Require Contractors to say they have liability insuran

[Ryan Smith]

So, i want all contractors to start signing a contract saying, among other things, No extra pay unless there is a change order approved.

Only thing I'm not sure about is should I require all contractors to say they have liability insurance? Many work for a big name company and do smaller contract jobs in the side with their skills. I know I've only done 1 house but I'm fortunate nobody filed a mechanic lien or got injured. That would've been bad! So knowing we want to do many, it's a good idea to be protected. What is reasonable knowing we still want to work with these independent contractors and still be protected?